PROGRESS OF PSYCHOLOGY. 459 



Verworn's researches are much more convincing, and 

 have been recently corroborated by H. S. Jennings.* 



In his study of the slipper animalcule (Para- 

 mcecium) and some other Protozoa, Jennings has 

 shown that in all the seeming to seek food or to evade 

 the inimical, there is but one typical motor reaction, 

 like that of a strip of muscle. It may be that a 

 vestige of consciousness persists and that the observ- 

 able reflex was once represented by a conscious im- 

 pulsive movement, but the fact seems to be that the 

 slipper animalcule now responds to all sorts of stim- 

 uli by one constant kind of movement. 



Reference should also be made to the psychological 

 study of some of the outstanding phenomena which 

 occur in the life of many different kinds of animals, 

 e.g., mating (Darwin, Wallace, Biichner, Lloyd 

 Morgan, Groos), or play (Groos). In a most in- 

 teresting study, Groos seeks to show that play is the 

 outcrop of instincts, evolved like other instincts from 

 congenital variations, and fostered in virtue of their 

 utility. But what can be the utility of play, which 

 by definition has no serious purpose ? To which it 

 is answered that play is the young form of work, a 

 rehearsal without responsibilities, that it lightens 

 the burden of inheritance by affording opportunity 

 for the exercise and perfecting of instinctive activi- 

 ties, and that the play period allows scope for the 

 rise and progress of new variations, initiatives, idio- 

 syncrasies, etc., which form the raw material of prog- 

 ress, before the struggle for existence has become 

 keen. 



Open Questions. We have elsewhere referred to 



* " Studies on Reactions to Stimuli in Unicellular Organisms." 

 Numerous papers in Amer, Journ. PhysioL and Amer. Naturalist, 

 from 1899 onwards. 



